At the time of inoculation, there are 4 sites that are inoculated along the stem of the trees.

We inoculate trees in early June. Preliminary selections for blight resistance are performed in November. Final selections are made in May, almost one year following the inoculation event.

For rating blight resistance, we use a scale from 1 to 5 with 1 being highly resistant and 5 being highly susceptible. The table below defines how one can rate a tree based on the relative size of cankers within an inoculated orchard.

Small cankers are the best and are given a "1" ranking. Ideally one would rate each individual canker; better yet, one would measure the length and width of each canker. Due to time constraints, however, we use a composite rating for the tree as a whole.

Chinese trees generally rate 1 or 2. F1 trees generally rate 3, and Americans generally rate 4-5. Because of environmental variation and its effects on inoculation reactions, checks are necessary to determine how a moderately resistance tree should look in any particular year. By comparing inoculated BC3 trees with an F1 tree, those BC3 trees with moderate resistance should act similar to the F1 checks. The others simply confirm that the inoculation technique performed as expected in any given year, adding relevance to the year's advance hybrid selection.

Scoring of Inoculation Sites

EP155 Size SG Size RATING
Small small 1
Medium small 2
Large small 3
X Large medium 4
XX Large large 5
  • For a tree to have a rating of 1, both SG and 155 cankers need to be very small, with complete closure of the wound by uninfected callus.
  • A tree with a rating of 2 will have 155 cankers not as above (not small), but not sunken with abundant sporulation.
  • A tree with a rating of a 3 willl have sunken 155 cankers with abundant sporulation, but the SG cankers will be small (<3.5cm long)
  • For a tree to garner a rating of 4, the SG cankers will not be small, but they will not be sunken with abundant sporulation.
  • A highly susceptible tree will be given a rating of 5 -- cankers of both inoculum types will be sunken with abundant sporulation.

There are also intermediate grades given, e.g. 2.5, 3.5, etc.

Ratings for American Chestnut Character

We select for American Characteristics based on the following criteria:

Select for these characteristics before the trees leaf out, sometime in March or early April would be appropriate.

BUD COLOR - black, yellow, red, brown
BUD SHAPE - round or cylindrical
BUD TIP - pointed or flat

* For More information on selection for these characters, see pdf below (Selection for Bud Characteristics)

BOAT: are the leaves generally shaped like a canoe?
ACUTE: is the leaf angle acute at the petiole?
DULL: is the leaf wax on top (adaxial) is dull?
BIG TOOTH: are the teeth on the leaf large?
TAPERED TOOTH: do the teeth taper to a point? (alternatively, they are wedge-shaped)
HOOK: do the teeth curve forward like a breaking ocean wave?
STIPNARROW: are the stipules 1mm wide or smaller?
STIPNOFLARE: are the stipules a uniform thickness top to bottom? (alternatively, they could flare out at the base like a Chinese)
NO LH: are there no leaf hairs underneath the leaf?
SPARSE VH: are the vein hairs sparse? (for more information, see Dr. Hebard's Journal of Heredity paper on morphological characters, citation below)

Hebard, FV. 1994. Inheritance of juvenile leaf and stem morphological traits in crosses of Chinese and American chestnut. The Journal of Heredity. Nov/Dec 1994. v. 85 (6) p. 440-446

BIG: is the tree big?
NOT EARLY: has the tree not been harmed by spring frost damage? This is usually assessed by branching at the same point around the crown in years with late spring frosts.
NICE BARK: is the bark normal and American looking? (alternatively, it could have Clapper or other defect). If normal, are the lenticels small?

* More information on rating a tree for American Chestnut Characteristics see excel file below ("Selection for American Characteristics")

Selection for Bud Characteristics

PDF document, 214.8 KB

Selection for American Chestnut Characteristics

Excel spreadsheet, 25.0 KB

Chestnut Selection Criteria

PDF document, 398.9 KB